A hardware system such as a refrigerator, a car, a watch, etc. is controlled in operation by a microcomputer mounted therein. In order to assist the development of such a hardware system, an in-circuit emulator which comprises an evaluation microcomputer and a memory for a program is used. The evaluation microcomputer evaluates a microcomputer mounted in a hardware system (defined "hardware system to be evaluated in operation" hereinafter). Even prior to the completion of a hardware to be evaluated in operation, therefore, the development and evaluation of a program to be stored in the hardware can be carried out in an in-circuit emulator by using an evaluation microcomputer and a memory included therein. In the development and evaluation of the program, terminals of the evaluation microcomputer must be set to be specifically high and low not to prevent the program form being executed.
For the other reason, most of microcomputers are designed by using CMOS process technology which is characterized in that power consumption is low. Due to the characteristics of CMOS devices, input terminals which are not connected to any terminals must be set to be specifically high and low.
A first conventional method for setting non-connected terminals of an evaluation microcomputer to be high and low is that the non-connected terminals are connected to an IC socket provided in an in-circuit emulator by a probe connected via a cable to the non-connected terminals.
A second conventional method for setting non-connected terminals of an evaluation microcomputer to be high and low is that the non-connected terminals are pulled up to a power supply and down to ground by using pull-up and down resistances.
A third conventional method for setting non-connected terminals of an evaluation microcomputer to be high and low is that the non-connected terminals are connected to a power supply and ground by using selectors.
However, there are disadvantages in the first to third conventional methods in that:
the size is large, the construction is complicated, and the cost is high in the first conventional method, because the IC socket is provided in an in-circuit emulator;
the electric characteristic is changed, and through-current flows through input gates to lower the reliability of a device in the second conventional method, because pull-up resistances connected to a signal line tends to differ in value from each other, and a potential on a signal line divided by resistances happens to turn both p- and n- transistors on; and
a number of selectors must be provided, and a signal propagation delay occurs in the third conventional method, because a selector is provided on each signal line.